A ground sentence contains no variables.
(<=> (Ground-Sentence ?Expression) (And (Sentence ?Expression) (Value-Type ?Expression Variables-In-Sentence Empty) (Value-Cardinality ?Expression Variables-In-Sentence 1)))
(Sentence ?Expression)
(Inherited-Facet-Value Slot-Value-Type Parametric-Constraint Constraint.Expression Ground-Sentence) (<=> (Parametric-Constraint ?Constraint) (And (Constraint ?Constraint) (Value-Type ?Constraint Constraint.Expression Ground-Sentence) (Value-Cardinality ?Constraint Constraint.Expression 1))) (<=> (Ground-Sentence ?Expression) (And (Sentence ?Expression) (Value-Type ?Expression Variables-In-Sentence Empty) (Value-Cardinality ?Expression Variables-In-Sentence 1)))